MDM2 is an important cancer-related protein that induces cancer cell survival and progression through both p53-dependent and -independent signaling pathways. In previous investigations of the p53-independent role of MDM2, we found that the oncoprotein MDM2 can increase the expression of the anti-apoptotic factor XIAP through binding of MDM2's RING domain to the XIAP IRES mRNA, inducing its translational activity. Our preliminary studies for this renewal application demonstrated that when XIAP IRES bound to the MDM2 RING domain protein, MDM2 protein stabilization increased. Based on these findings, we believe that the binding action between XIAP IRES and the RING domain of MDM2 can simultaneously increase expression of XIAP and MDM2, through activation of IRES-dependent translation and by inhibition of protein degradation, respectively. In cancer cells, increased expression of both MDM2 and XIAP may aid cancer progression or resistance to anticancer treatment. Accordingly, we hypothesized that inhibition of this molecular interaction would result in a simultaneous decrease in the expression of both MDM2 and XIAP, leading to not only suppression of the cancer, but a reversal of drug resistance during therapy. The goals of this project are: to identify small molecule inhibitors that can disrupt the MDM2 protein/XIAP IRES interaction, to characterize whether the identified MDM2/XIAP inhibitors are able to induce MDM2 self-ubiquitination and degradation as well as inhibition of XIAP translation, and to ascertain the potential use of the identified inhibitors as new drugs able to treat refractory cancer patients. Specifically, Aim 1 is to perform HTS to select small-molecule compounds that block or disrupt the interaction between XIAP IRES mRNA and the RING domain protein of MDM2; Aim 2 will investigate how selected MDM2/XIAP inhibitors disrupt that interaction at the molecular level and find the mechanism of action by which the inhibitor targets MDM2 degradation. For Aim 3, we will examine the effects of MDM2 degradation and inhibition of XIAP translation by selected compounds on cancer cell growth and apoptosis in vitro, plus perform translational studies in animal models to ascertain these identified compounds as clinically viable anticancer drugs. Because a significant number of cancer patients have malignant cells that are overexpressing MDM2 and XIAP and their survival remains poor, we hope our studies will lead directly to the discovery of several useful new drugs to treat these refractory cancer patients.